Medical drug delivery devices are used to deliver selected doses of medication to patients. Some medication, such as insulin is self-administered. The typical diabetes patient will require injections of insulin several times during the course of the day.
State of the art drug delivery devices, such as the injection device disclosed in WO 01/95959, provides a user friendly and accurate device wherein most demands as regards patient needs are met. However, purely mechanical working injection devices do not provide the possibility of storing information related to previously injected doses for later retrieval.
Some prior art devices, such as the injection device shown in WO 02/92153, include an electronic dose size identifier and an electronic display which can be used to display the size of a currently set dose as well as the dose size of previously injected doses.
In order to provide more user friendly devices the dosage selector of the injection device should preferably include a rotatable dosage selector which can be dialled in very fine increments. In particular in injection devices for delivery of half-incremental units of a medication, the incremental steps when rotating from one dose size to the next consecutive dose size should preferably be very small. This is of particular importance when dialling larger doses which otherwise usually results in the need of rotating the dosage selector several full revolutions. Such “endless” turning typically will be considered as incurring an unnecessary discomfort. The trend of minimizing incremental dose setting steps in drug delivery devices introduce an increase in the demands regarding the accuracy of the detection system for detecting dose sizes.
Another problem with prior art drug delivery devices, is that monitoring of the end of dose condition, i.e. the specific state where a dosing action is fulfilled, may be somewhat imprecise or unreliable, having consequences for the correct monitoring of dose information.
Another problem when designing different versions of an injection device so as to provide different dose increments for different versions, e.g. full incremental devices and half-incremental devices, is that normally, a large number of components have to be redesigned in order for both versions to perform adequately.
Having regard to the above-identified prior art devices, it is an object of the present invention to provide a drug delivery device which enables improved electronic detection of movements in an injection device.
A further object of the invention is to provide an electronic drug delivery device, which optionally can be equipped with means for transferring data with an external device, where the drug delivery device incorporates a power-management which is effective in minimizing power consumption for the incorporated electronic circuitry, yet allows ease of use during operation of the device.
Yet a further object of the invention is to provide measures for obtaining devices having a superior performance and, at the same time, being manufactured at a reduced cost.